Fire type is an extremely good offensive type. Steel types are abundantly common in OU (I'm assuming this is OU) because of their high amount of potential. Grass type usage is also common. Blaze Kick may not be great for Ferrothorn because of Iron Barbs, but it will definitely do a sizable chunk to them if you manage to get one off.
Why not the others?
As you've mentioned, Hydreigon is also a common opponent. However, you have Close Combat for Dark types. I personally believe Fake Out is more or less a waste of a move slot, because it can only be used on the first turn. It does have it's uses though; such as breaking Focus Sashes or just getting that extra bit of damage crucial to the OHKO.
Overall, it just depends on what your team needs. If your team has less Fire coverage, then use Blaze Kick. If you have no Fairy types, then use Play Rough. Try to complement the rest of your team.